Cell phones emit "non-ionizing electromagnetic radiation" (the kind that comes from microwaves), not "ionizing radiation" (the kind that comes from X-rays). And it turns out that's an important difference.

"Exposure to ionizing radiation, such as from radiation therapy, is known to increase the risk of cancer," the National Cancer Institute explains, although even there, the dose matters a lot. "However, although many studies have examined the potential health effects of non-ionizing radiation from radar, microwave ovens, and other sources, there is currently no consistent evidence that non-ionizing radiation increases cancer risk."

While people spend much more time with their cell phones than their microwaves, it's still hard to get a good idea of the dose of non-ionizing radiation we get from them. The amount of radiation absorbed by individuals will vary depending on the kind of phones they have and how they use them.

A lot of uncertainty also comes from improved cell phone technology and increased usage over the years — the research just can't keep up.

The Research So Far

"Studies thus far have not shown a consistent link between cell phone use and cancers of the brain, nerves, or other tissues of the head or neck," the National Cancer Institute notes on their website. But their fact sheet addressing the topic is not conclusive for the reasons above.

Since proximity is so important in radiation exposure, most research has looked for links between cell phones and brain cancer specifically, which only represents 2% of all cancers.

Between 2006 and 2010, there were 6.5 cases of brain cancer per 100,000 people, though rates are significantly higher in those over 65 (19.4 per 100,000). Since the risk is so small, even if researchers were to find conclusively that cell phones double that risk — something they certainly have not shown — the risk of brain cancer would still be much smaller than that for other more common cancers.

What's Next

While the research has been inconclusive so far, scientists are working to figure out if there is a link between cancer and cell phone use — or if such a link can be ruled out.

One study in the U.K., known as COSMOS, began in 2010 and will follow 290,000 cell phone users for 20-30 years. Researchers will have access to participants' phone records, which should give a much more reliable picture of usage than previous studies, which relied largely on people's recollections of their cell phone usage from many years ago.

Such ongoing research will be crucial.

"It often takes many years between the use of a new cancer-causing agent — such as tobacco — and the observation of an increase in cancer rates," Dr. John Moynihan, of the Mayo Clinic, points out. "At this point, it's possible that too little time has passed to detect an increase in cancer rates directly attributable to cellphone use."